The invention relates to detecting thread wear in screw-nut assemblies, and in particular in screw actuators.
More precisely, the invention relates to such detection when it is implemented by means of an electrical wear sensor.
Detecting thread wear is an important concern, particularly when it seeks to give warning about a strength limit for the screw-and-nut pair.
Predicting possible breakage is a concern that is particularly strong in the field of screw actuators, i.e. systems in which a screw and a nut are caused to rotate relative to each other in repeated manner, for the purpose on each occasion of transforming such rotation into mutual thrust or traction.
More generally, wear detection seeks to indicate that the screw-and-nut pair is operating in a manner considered to be normal.
Document SU 1 490 586 describes a probe placed in a ring having the same diameter as the nut, and secured thereto in a position on the same axis, the ring also bearing against the thread of the screw so that it is itself subjected to wear.
The electrical probe that responds to coming into contact with the screw is buried in the ring so as to become flush with the wear zone thereof. Excessive wear of the ring is considered as being indicative of the need to perform maintenance.
Nevertheless, that system remains unsatisfactory since the ring is complex to make and time consuming to put into position.
Furthermore, its reliability in measurement is insufficient.
The object of the invention is thus to solve those drawbacks.
This object is achieved by means of a screw-and-nut assembly comprising a support secured to the nut, which support is provided with a surface in contact with the thread of the screw, and an electrical sensing member responsive to mechanical interaction with the thread of the screw, the sensing member being placed in the support close to said surface to come into interaction with the thread of the screw in the event of said surface wearing, wherein the support and the nut are constituted by the same block of material, the sensing member thus being placed inside the nut.
The invention also provides a screw actuator including such a screw-and-nut assembly.
The invention provides an actuator of the type including a screw, a primary nut transmitting the force of the actuator in normal operation, and a secondary nut that acts to take over the force of the actuator in the event of the primary nut failing, the pair formed by the screw and the secondary nut being in accordance with the above-specified definition.